<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .outside {
            background-image: url("image/5.jpg");
            background-repeat: no-repeat;
            background-position: top center;
            height: 2108px;
        }

        .main {
            margin: 0 auto;
        }
        .main {
            background-image: url("image/4.jpg");
            height: 1108px;
            width: 1000px;
            background-repeat:no-repeat;
            /*
            center
            top
            bottom
            left
            right
            */
        }
        .login {
            background-color: white;
            width: 500px;
            height: 300px;
            position: absolute;
            top: 800px;
            left:260px;
        }
    </style>
</head>
<body>
<div class="outside">
    <div class="main">
        <div class="login">
            <form>
                用户名：<input>
            </form>
        </div>
    </div>
</div>

</body>
</html>